Lake Pueblo Park has a fascinating geologic history shaped by three key processes:

1. Deposition of sedimentary rocks: During the Cretaceous Period, an inland sea covered the region, collecting sediments from western mountains (present-day Nevada). Over time, these sediments formed rock layers of sandstone, shale and limestone, preserving plant and animal fossils.
    
2. Uplift and mountain building: Toward the end of the Cretaceous, the Rocky Mountains uplifted, creating the ranges west of Lake Pueblo and elevating the eastern high plains. The Tertiary period, which followed the Cretaceous, witnessed the deposition of non-marine sediments on the high plains, originating from the uplifting Rockies.
    

3. Erosion and landscape evolution: In the Tertiary, river systems developed, including the Arkansas, which carved the valley now occupied by Lake Pueblo. This erosion shaped steep bluffs on the lake's north and south sides, exposing sedimentary rocks from the Cretaceous.

   Notable rock layers in the park include Dakota Sandstone, Graneros Shale, Lincoln Limestone, Hartland Shale, Bridge Creek Limestone, Fairport Chalky Shale, Blue Hill Shale, Codell Sandstone and Ft. Hayes Limestone. These can be observed along the dam spillway, through Rock Canyon and up to the Liberty Point area.

   Lake Pueblo's Rock Canyon is a global reference point, Global Boundary Stratotype Section and Point (GSSP), for a specific boundary on the geologic time scale. Geologists worldwide visit to study this site. Although fossils are common, collecting rocks or fossils is prohibited in the park.